Ripple count circuit

ABSTRACT

A motor control system includes a variable voltage supply in signal communication with a direct current (DC) motor. The DC motor includes a rotor induced to rotate in response to a drive current generated by a variable supply voltage delivered by the voltage supply. The rotation of the rotor ( 103 ) generates a mechanical force that drives a component. A ripple count circuit ( 104 ) is configured to filter the drive current based on a rotational speed (ω) of the rotor ( 103 ), and to generate a pulsed output signal indicative of the rotational speed (ω) of the rotor and a rotational position (θ) of the rotor.

TECHNICAL FIELD

Exemplary embodiments of the present disclosure are related to directcurrent (DC) motors, and more particularly, to DC motors for operatingelectrically operated automotive components.

BACKGROUND

Automobile vehicles are increasingly equipped with electrically operatedcomponents. For example, vehicles typically include sliding roofs,window glass regulators, or rear view mirrors driven by electric DCmotors. Information indicating the rotor speed of the motor can beutilized to determine a position of the component (e.g., the window).Conventional position measurement systems utilize a sensor inconjunction with a magnetic ring to determine the rotor speed of themotor. For example, a Hall Effect Sensor (HES) detects movements of amagnetic ring integrated with the rotor. The magnet ring generates amagnetic flux of varying strength towards the HES depending on therelative axial position of the magnetic ring and sensor. The magneticflux induces a current, and variations in magnetic flux result invariations in the induced currents. Accordingly, the frequency of thecurrent measured by the HES is indicative of the rotor speed of the DCmotor.

SUMMARY OF THE INVENTION

According to a non-limiting embodiment, a motor control system includesa variable voltage supply in signal communication with a direct current(DC) motor. The DC motor includes a rotor induced to rotate in responseto a drive current generated by a variable supply voltage delivered bythe voltage supply. The rotation of the rotor generates a mechanicalforce that drives a component. A ripple count circuit is configured tofilter the drive current based on a rotational speed (ω) of the rotor,and to generate a pulsed output signal indicative of the actualrotational speed (ω) of the rotor and an actual rotational position (θ)of the rotor.

According to another non-limiting embodiment, a ripple count circuitcomprises an amplifier, a current differential circuit, a bandwidthfilter, a downstream low pass filter, and a comparator circuit. Theamplifier is configured to amplify a drive current that drives rotationof a rotor included in a direct current (DC) motor. The currentdifferential circuit is configured to generate a derivative currentsignal that indicates an instantaneous rate of current change (d(i)/dt))of the drive current. The bandwidth filter is configured to filter thederivative current signal based on a rotational speed (ω) of the rotorso as to output a first filtered signal. The downstream low pass filteris configured to filter the first filtered signal based on therotational speed (ω) of the rotor so as to output a second filteredsignal that eliminates harmonics from the first filtered signal. Thecomparator circuit is configured to compare the second filtered drivecurrent to a reference voltage potential, and generate a pulsed outputsignal having a first output voltage level when a voltage level of thefilter drive current is greater than or equal to the reference voltagepotential, and a second output voltage level when a voltage level of thefilter drive current is less than the reference voltage potential. Thepulsed output signal indicates the actual rotational speed (ω) of therotor 103 and an actual rotational position (θ) of the rotor.

According to yet another non-limiting embodiment, a method ofdetermining a rotor speed of a direct current (DC) motor comprisesgenerating a variable supply voltage, inducing a drive current based onthe variable supply voltage, and rotating a rotor included in the DCrotor based on the drive current. The method further comprisesgenerating a mechanical force in response to rotating the rotor to drivea component, and filtering the drive current based on a rotational speedof the rotor. The method further comprises generating a pulsed outputsignal indicative of the actual rotational speed (ω) of the rotor 103and an actual rotational position (θ) of the rotor.

The above-described and other features and advantages of the presentinvention will be appreciated and understood by those skilled in the artfrom the following detailed description, drawings, and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 is a schematic diagram of a motor control system including aripple count circuit according to a non-limiting embodiment;

FIG. 2 is a signal diagram illustrating the output of an amplificationstage included in the ripple count circuit of FIG. 1 according to anon-limiting embodiment;

FIG. 3 is a signal diagram illustrating the output of a low pass filterstage included in the ripple count circuit of FIG. 1 according to anon-limiting embodiment;

FIG. 4 is a signal diagram illustrating the output of a bandwidth filterstage included in the ripple count circuit of FIG. 1 according to anon-limiting embodiment;

FIG. 5 is a signal diagram illustrating the output of a downstream lowpass filter stage located downstream from the bandwidth filter stageincluded in the ripple count circuit of FIG. 1 according to anon-limiting embodiment; and

FIG. 6 is a signal diagram illustrating a square wave output from theripple count circuit of FIG. 1, and indicative of a rotational rotorposition (θ) and rotational rotor speed (ω) associated with a motorcontrolled by the motor control system of FIG. 1 according to anon-limiting embodiment.

DETAILED DESCRIPTION

Conventional DC motor position systems utilizing a HES and a magneticring are expensive and complex. In addition, the frequency of themeasured flux must be further computed resulting in longer times neededto determine the corresponding rotor speed. Attempts to overcome thedisadvantages of the HES and magnetic ring have led to the utilizationof highly expensive digital controllers that perform complex algorithmssuch as a fast Fourier transform, for example, to calculate the rotorspeed based on the electrical current driving the DC motor.

Various non-limiting embodiments described herein provide a ripple countcircuit configured to determine a rotor speed of a DC motor based on aresidual ripple current. During operation of the DC motor, a stationaryenergy unit, sometimes referred to as a stator or field winding, isenergized with electrical current. The current flowing through the fieldwinding generates a magnetic field that induces rotation of a rotor,sometimes referred to as a rotating armature. The armature currentsignal generated in response to the rotation includes a DC signalcomponent and an alternating current (AC) signal component superimposedon the DC signal component. The ripple count circuit according to one ormore embodiments described herein is configured to extract the AC signalfrom the armature current signal without the use of an expensivecontroller or a combination of a magnetic ring and HES as required byconventional DC motor position systems. The extracted AC signal can thenbe utilized to generate a pulsed signal or square-wave, which indicatesthe actual rotational speed and the actual rotational position of therotor.

Referring now to FIG. 1, a motor control system 100 is illustratedaccording to a non-limiting embodiment. The motor control system 100includes a motor 102 and a ripple count circuit 104. The motor 102includes a DC motor 102, which is in signal communication with a powersupply 106. The power supply 106 can include, for example, an electronichardware controller 106 which outputs a variable supply voltage (+Vcc).

The DC motor 102 includes a rotor 103 induced to rotate in response to adrive current generated by the variable supply voltage (+Vcc). Therotation of the rotor 103 generates a mechanical force that drives acomponent 108. Going forward, the component 108 will be described interms of an automotive vehicle window regulator unit 108. It should beappreciated, however, that other components 108 can be driven by the DCmotor 102 including, but not limited to, a sliding roof, rear viewmirrors, etc. In terms of a window glass regulating unit 108, the DCmotor 102 can drive various mechanical components to vary the positionof a glass window (e.g., move the window up or down). The input supplyvoltage (+Vcc) can be actively controlled to vary the voltage levelapplied to the DC motor 102, thereby adjusting the speed of the rotor103, and thus the speed at which to move the glass window. A shuntresistor 105 can be connected to the output terminal of the motor 102 tomeasure AC or DC electrical drive current based on the voltage drop thedrive current produces across the resistor 105.

The ripple count circuit 104 includes an amplifier 110, a low passfilter 112, a current differential circuit 114, a bandwidth filter 116,a downstream low pass filter 118, and a comparator circuit 120. Theripple count circuit 104 is configured to filter the drive current basedon the rotational speed (ω) of the rotor 103, and to generate a pulsedoutput signal indicative of the actual rotational speed (ω) and anactual rotational position (θ) of the rotor 103.

The amplifier 110 includes an input that is connected in common with theoutput terminal of the motor 102 and the input terminal of the shuntresistor 105. Various amplifiers can be used including, but not limitedto, an operation amplifier circuit (Op-Amp). In this manner, theamplifier 110 receives the drive current and generates an amplifieddrive current signal (I_(MOTOR)) as illustrated in FIG. 2.

The low pass filter 112 includes an input terminal that is connected tothe output of the amplifier 110 to receive the amplified drive currentsignal (I_(MOTOR)). The low pass filter 112 can be constructed as asecond-order low pass filter having a frequency cutoff set, for example,at about 1 kilohertz (1 KHz). Accordingly, the low pass filter 112outputs a smoothened or filtered drive current signal (I_(FILTER)) asillustrated in FIG. 3.

The current differential circuit 114 includes an input that is connectedto the output terminal of the low pass filter 112 to receive thefiltered drive current signal (I_(FILTER)). The current differentialcircuit 114 can be constructed as an inductor, for example. Accordingly,the output of the current differential circuit 114 (e.g., the inductor)determines the derivative of the filtered drive current signal, i.e.,I_(FILTER)′, which indicates the instantaneous rate of current change(d(i)/dt)) having measured units of amps per second.

The bandwidth filter 116 includes an input that is connected to theoutput terminal of the current differential circuit 114 to receiveI_(FILTER)′. The bandwidth filter 116 can be constructed as any variablecenter frequency bandwidth filter capable of actively varying its centerfrequency (fo). In at least one embodiment, the controller 106 generatesa center frequency control signal indicative of the center frequency(fo), and the bandwidth filter 116 is a digital bandwidth filter thatactively varies its center frequency (fo) based on the center frequencycontrol signal output from the controller 106.

The bandwidth filter 116 filters I_(FILTER)′ according to a bandwidthhaving a center frequency (fo) that is dynamically (i.e., actively) setaccording to an estimated rotational speed (ω) of the rotor 103. Thus,the center frequency (fo) of the bandwidth filter 116 is dynamicallyadjusted or varied as the rotor speed (ω) changes. Accordingly, thebandwidth filter 116 outputs a bandwidth filtered signal (I_(BW)) asillustrated in FIG. 4. In at least one embodiment, the presentrotational speed (ω) of the rotor 103 can be estimated based on themeasured voltage of the motor 102 and the measured current of the motor102. For example, each time the motor 102 is powered, the startingvoltage (U_(a)) and the starting current (I_(a)) can be measured, andwhile operating, the motor voltage (U_(m)) and motor Current (I_(m)) canalso be measured. The measurements can be performed by the controller106 and/or various sensors installed on the motor 102. The motorinternal resistance, i.e.,

${R_{i} = \frac{U_{a}}{I_{a}}},$

can be calculated, e.g., by the controller 106, while the magnetic flux(Φ) of the motor 102, the number of winding turns (n) of the motor 102,and the number of motor slots (S_(m)) of the motor 102 are knownconstants. The inductance value (L) of the motor 102, and the motorconstant (K) are also known constants. Therefore, the estimated rotorspeed (ω) can be calculated as:

$\begin{matrix}{\omega = \frac{U_{m} - {R_{i} \times I_{m}} - {L\frac{d\left( I_{m} \right)}{dt}}}{K \times n \times \varnothing}} & {{eq}.\mspace{14mu} 1}\end{matrix}$

In turn, the bandwidth filter center frequency (fo) can be calculated,e.g., by the controller 106, as:

$\begin{matrix}{f_{O} = \frac{\omega}{2\pi \times S_{m}}} & {{eq}.\mspace{14mu} 2}\end{matrix}$

The downstream low pass filter 118, includes an input terminal that isconnected to the output of the bandwidth filter 116 to receive thebandwidth filtered signal (I_(BW)). The downstream low pass filter 118can operate according to a dynamically varying frequency cutoff (fc).The downstream low pass filter 118 can be constructed as any active lowpass filter capable of actively varying its frequency cutoff (fc). In atleast one embodiment, the controller 106 outputs a frequency cutoffcontrol signal that indicates the (fc), and the downstream low passfilter 118 is a digital low pass filter that actively varies itsfrequency cutoff (fc) based on a frequency cutoff control signal outputfrom the controller 106.

The frequency cutoff (fc) can be dynamically (i.e., actively) setaccording to the estimated rotational speed (ω) of the rotor 103. Basedon the estimated rotational speed (ω) described above, the cutofffrequency (fc) can be calculated, e.g., by the controller 106, as:

$\begin{matrix}{f_{c} = \frac{\omega}{2\pi}} & {{eq}.\mspace{14mu} 3}\end{matrix}$

Accordingly, the downstream low pass filter 118 generates a filtered ACbandwidth signal (BW_(FILTERED)) shown in FIG. 5, which removes theremaining harmonics previously found in the initial bandwidth signal(see FIG. 4).

The comparator circuit 120 is configured to compare the filtered ACbandwidth signal (BW_(FILTERED)) to a references value. Based on thecomparison, the comparator circuit 120 outputs a pulsed signal or squarewave (ROTOR) indicative of the rotational position (θ) and rotationalspeed (ω) of the rotor 103, as illustrated in FIG. 6. In at last oneembodiment, the comparator circuit 120 is constructed as a differentialamplifier that includes a pair of input terminals. A first inputterminal is connected to the output of the downstream low pass filter118 to receive the filtered AC bandwidth signal (BW_(FILTERED)). Thesecond input terminal is connected to a reference potential such as, forexample, ground (i.e., 0 V).

The comparator 120 compares the amplitude of the filtered AC bandwidthsignal (BW_(FILTERED)) to the reference value applied to the secondterminal (e.g. 0 V). The reference value can serve as a fixed ripplethreshold (THR) that determines whether the pulsed signal at given timewill be output at first voltage level or a second voltage level. Forexample, when the difference between the filtered AC bandwidth signal(BW_(FILTERED)) and the reference value is positive, the comparator 120generates a first voltage output (e.g., 5 V). When, however, thedifference between the filtered AC bandwidth signal (BW_(FILTERED)) andthe reference value is negative, the comparator 120 generates a secondvoltage output (e.g., 0 V). Accordingly, the comparator circuit 120outputs the square wave (ROTOR) which indicates the rotational position(θ) and rotational speed (ω) of the rotor 103 without the use of anexpensive controller or a combination of a magnetic ring and HES asrequired by conventional DC motor position systems.

In at least one embodiment, the square wave (ROTOR) can be delivered tothe controller 106 to indicate the rotor position (θ) and rotor speed(ω). Based on the square wave (ROTOR), the controller 106 can adjust theinput supply voltage (+Vcc) applied to the motor 102, which in turnvaries the motor drive current and thus the mechanical output of themotor 102. In the example described herein, the controller 106 cantherefore use the square wave (ROTOR) to vary the drive current, therebycontrolling the speed at which to move the position of the glass window106.

As described herein, various non-limiting embodiments described hereinprovide a motor control system configured to measure a rotor speed of aDC motor. Unlike conventional DC motor position systems which utilizeexpensive microcontroller or complex arrangements of a HES and magneticring, the motor control system according to at least one embodimentincludes a ripple count circuit that extracts the AC ripple current fromthe motor drive current, and generates a square wave indicative of therotor speed and rotor position.

As used herein, the term “module” refers to an application specificintegrated circuit (ASIC), an electronic circuit, a microprocessor, acomputer processor (shared, dedicated, or group) and memory thatexecutes one or more software or firmware programs, a combinationallogic circuit, a microcontroller including various inputs and outputs,and/or other suitable components that provide the describedfunctionality. The module is configured to execute various algorithms,transforms, and/or logical processes to generate one or more signals ofcontrolling a component or system. When implemented in software, amodule can be embodied in memory as a non-transitory machine-readablestorage medium readable by a processing circuit (e.g., a microprocessor)and storing instructions for execution by the processing circuit forperforming a method. A controller refers to an electronic hardwarecontroller including a storage unit capable of storing algorithms, logicor computer executable instruction, and that contains the circuitrynecessary to interpret and execute instructions.

As used herein, the terms “first,” “second,” and the like, herein do notdenote any order, quantity, or importance, but rather are used todistinguish one element from another, and the terms “a” and “an” hereindo not denote a limitation of quantity, but rather denote the presenceof at least one of the referenced item. In addition, it is noted thatthe terms “bottom” and “top” are used herein, unless otherwise noted,merely for convenience of description, and are not limited to any oneposition or spatial orientation.

The modifier “about” used in connection with a quantity is inclusive ofthe stated value and has the meaning dictated by the context (e.g.,includes the degree of error associated with measurement of theparticular quantity).

While the invention has been described with reference to an exemplaryembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A motor control system comprising: a controller configured togenerate a variable supply voltage; a direct current (DC) motorincluding a rotor induced to rotate in response to a drive currentgenerated by the variable supply voltage, the rotation of the rotorgenerating a mechanical force that drives a component; and a ripplecount circuit configured to filter the drive current based on arotational speed (ω) of the rotor to generate at least one filtereddrive current, and to generate a pulsed output signal indicative of therotational speed (ω) of the rotor and a rotational position (θ) of therotor.
 2. The motor control system of claim 1, wherein the ripple countcircuit compares the at least one filtered drive current to a referencevoltage potential, outputs the pulsed output signal having a firstoutput voltage level when a voltage level of the at least one filtereddrive current is greater than or equal to the reference voltagepotential, and outputs the pulsed output signal having a second outputvoltage level when a voltage level of the at least one filtered drivecurrent is less than the reference voltage potential.
 3. The motorcontrol system of claim 1, wherein the ripple count circuit includes abandwidth filter having variable center frequency (fo) that is activelyset according to the rotational speed (ω) of the rotor so as to filterthe drive current based on the rotational speed (ω) of the rotor.
 4. Themotor control system of claim 3, wherein the ripple count circuitincludes a downstream low pass filter disposed downstream from thebandwidth filter, the downstream low pass filter configured to eliminateharmonics from the filtered drive current.
 5. The motor control systemof claim 4, wherein the downstream low pass filter has varying frequencycutoff that is actively set according to the rotational speed (ω) of therotor.
 6. The motor control system of claim 1, wherein the controllervaries a voltage level of the variable supply voltage based on at leastone of the rotational speed (ω) and the rotational position (θ)indicated by the pulsed output signal.
 7. A ripple count circuitcomprising: an amplifier configured to amplify a drive current thatdrives rotation of a rotor included in a direct current (DC) motor; acurrent differential circuit configured generate a derivative currentsignal that indicates an instantaneous rate of current change (d(i)/dt))of the drive current; a bandwidth filter configured to filter thederivative current signal based on a rotational speed (ω) of the rotorso as to output a first filtered signal; a downstream low pass filterconfigured to filter the first filtered signal based on the rotationalspeed (ω) of the rotor so as to output a second filtered signal thateliminates harmonics from the first filtered signal; and a comparatorcircuit configured to compare the second filtered signal to a referencevoltage potential, and generate a pulsed output signal having a firstoutput voltage level when a voltage level of the second filtered signalis greater than or equal to the reference voltage potential, and asecond output voltage level when a voltage level of the second filteredsignal is less than the reference voltage potential, wherein the pulsedoutput signal indicates the rotational speed (ω) of the rotor and arotational position (θ) of the rotor.
 8. The ripple count circuit ofclaim 7, wherein the bandwidth filter has variable center frequency (fo)that is actively set according to the rotational speed (ω) of the rotorso as to filter the derivative current signal based on the rotationalspeed (ω) of the rotor.
 9. The ripple count circuit of claim 7, whereinthe downstream low pass filter filters the first filtered signalaccording to a varying frequency cutoff that is actively set accordingto the rotational speed (ω) of the rotor.
 10. A method of determining arotor speed of a direct current (DC) motor, the method comprising:generating a variable supply voltage; inducing a drive current based onthe variable supply voltage, and rotating a rotor included in the directcurrent (DC) motor based on the drive current; generating a mechanicalforce in response to rotating the rotor to drive a component; filteringthe drive current based on a rotational speed of the rotor to generateat least one filtered drive current; and generating a pulsed outputsignal indicative of the rotational speed (ω) of the rotor and arotational position (θ) of the rotor.
 11. The method of claim 10,wherein generating the pulsed output signal comprises: filtering thedrive current; comparing the at least one filtered drive current to areference voltage potential; outputting the pulsed output signal havinga first output voltage level when a voltage level of the at least onefiltered drive current is greater than or equal to the reference voltagepotential; and outputting the pulsed output signal having a secondoutput voltage level when a voltage level of the at least one filtereddrive current is less than the reference voltage potential.
 12. Themethod of claim 10, wherein filtering the drive current comprisesperforming a first filtering operation on the drive current, the firstfiltering operating including a bandwidth filtering operation thatfilters the drive current based on a varying center frequency that isactively set based on the rotational speed (ω) of the rotor.
 13. Themethod of claim 12, wherein filtering the drive current furthercomprises performing a second filtering operation following the firstfilter operation to eliminate harmonics from the at least one filtereddrive current.
 14. The method of claim 13, wherein the second filteringoperation includes performing a low pass filtering operation based on afrequency cutoff that is actively set according to the rotational speed(ω) of the rotor.
 15. The method of claim 10, further comprisingactively adjusting a voltage level of the variable supply voltage basedon at least one of the rotational speed (ω) and the rotational position(θ) indicated by the pulsed output signal.